1. Field of the Invention
The present invention relates to electrostatic printing rolls, and their preparation, by magnetically forming an image of nonconductive toner on a conductive image bearing magnetic roll followed by transfer of the toner to a conductive substrate to form the electrostatic printing roll. The areas of the electrostatic printing charged while the charge is dissipated from the conductive nonimage areas. The charged nonconductive areas are decorated with an oppositely charged toner containing a colorant such as a dye or pigment, which toner is then transferred to a substrate and permanently fixed thereto.
2. Description of the Prior Art
Magnetic printing processes, particularly useful in overcoming the problem in electrostatic copying processes of unsatisfactory copying of large dark areas, are known in the art. Such processes are described, for instance, in U.S. Pat. Nos. 4,099,186 and 4,117,498. The particular processes described in U.S. Pat. Nos. 4,099,186 and 4,117,498 relate to processes wherein a dye and/or other chemical treating agent contained in a ferromagnetic toner is transferred directly to a substrate, e.g., such as a textile material, or is transferred to a first substrate such as paper for subsequent transfer to the ultimate substrate. However, all these techniques relied on removal of the resin and magnetic components of the toner from the substrate after dyeing, hence, eliminating the use of this technique in the pigment printing of textiles.
More recently magnetic printing has been used to form the resist when preparing printed circuits or printing plates by etching or plating, or to produde lithographic plates directly. Such processes are described in U.S. Pat. No. 4,292,120 and U.S. Ser. No. 173,871, filed July 30, 1980, now U.S. Pat. No. 4,338,391.
A serious problem in the prior art is that magnetically attractive toners are not provided in a variety of colors but are generally black, dark reddish brown or a dark bluish black. Thus, an image through color magnetography, while theoretically possible, it is impractical in the present state of the technology.